David Clensy meets the screenwriter working on the first modern war film to look at the British Army's experience in Afghanistan – and he has chosen a haunting true story of heroism in the field

It is a world away from the dusty plains of Helmand Province.

Tom Williams' farmhouse, set on a lush green Wiltshire hillside, outside the village of Norton Bavent, near Warminster, is a tranquil spot.

But as I step out of my car and crunch across the pebbles of his drive, yards away young Army recruits are being put through their paces, splattering their way up the muddy lane on a cross-country run.

The more experienced soldiers striding up the hill past the new boys have almost certainly served under the arduous Afghan sun. There is something in their creased frowns as they run past that betrays the experience.

With the withdrawal of British troops from Afghanistan planned for later this year, the recruits running up the hill know they will probably never be concerned by the pressures of daily life serving in that remote, war-torn nation, where suicide bombers and IEDs (improvised explosive devices) are as much of a constant enemy as actual "insurgents".

Inside the farmhouse, Tom Williams is hard at work on his latest project.

For months now, his mind has been far from the green farmland around him, concentrating instead on one particularly grim day in Helmand in 2006.

The film screenwriter's credentials don't automatically suggest he would be best-suited to penning the first war film based on the British Army's experience in Afghanistan. His best-known production to date was the "frothy" (to use his own word) rom-com Chalet Girl.

But growing up in the Wiltshire garrison town of Tidworth, the son of a soldier, Tom feels a part of the wider Army family.

It was when he moved to his current home, so close to the network of MoD bases in nearby Warminster, that his mind first turned to writing a war film.

"It struck me that there weren't any modern British war films about Afghanistan or Iraq, and I wondered why that was," he says, as he brews the coffee. "We had so many war films after the Second World War – then it was almost a way of getting people through the tough times of the late 1940s and saying, look, it was all worth it.

"But these modern wars have been more politically charged than the Second World War. That was much more clearly black versus white, when you had Nazis fighting against us.

"The film industry in this country has been much more cautious about exploring modern conflict, ever since the days of the Falklands, if you think about it.

"That's certainly not been the case in America," Tom adds, "where both Hollywood and the US public are much more open to recording the experiences of their armed forces – whether it was with all those Vietnam films, or more recently with movies about Americans serving in Iraq and Afghanistan.

"There's a film out now over there called Lone Survivor, with Mark Wahlberg, which is a prime example."

Keen to find a suitable subject matter for a modern British war movie, Tom looked no further than his newspaper, where the inquest of Corporal Mark Wright was unfolding at the time his attention first turned to the idea in 2008.

"I began to realise what an extraordinary story it was. This group of 12 paratroopers who were out on reconnaissance near a dam in Helmand, called the Kajaki dam, when they found themselves in the most horrendous situation.

"They wandered on to a dry riverbed, where scores of mines, left behind from the earlier Russian war, had been washed down from the valley sides and had clustered in one stretch of mud.

"These paras found themselves trapped, completely surrounded by mines. One stood on a mine – one of the medics – and another medic used his rucksack as blast protection, allowing him to reach his friend to give medical attention. That kind of bravery is extraordinary.

"There is a political story in there too," Tom says, "about the equipment these guys had, failing batteries in the radios for instance, insufficient kit to deal with the mines, insufficient information telling them the minefield was there in the first place.

"But I was never interested in making this movie a political exercise. I just wanted to tell the human story of these 12 men, trapped in one location, unable to move for fear they would be the one to tread on a mine next."

One by one the mines were picking them off as they attempted to get out of the riverbed, and when they were eventually able to radio for help, they expected the military to send in a small helicopter to lift them out.

"Instead, it sent in a Chinook," Tom explains. "And although there is some dispute about this, many of the survivors believe it was actually the down-draught from the rescue helicopter that detonated the final mine, which killed Corporal Mark Wright. He was an extraordinary man. Even after he'd been wounded by the mine, he led the rescue mission, lifting the men's spirits, while all the time he was slowly bleeding to death."

It's little surprise then, that Corporal Wright posthumously received the George Cross for his gallantry.

Tom teamed up with director Paul Katis, whom he had worked with for a number of years, mostly on low budget corporate health and safety films.

"We'd done one a few years before for the British Army, warning soldiers about the dangers they faced with their equipment," Tom explains.

"For that we interviewed soldiers who had been unfortunate enough to have industrial accidents on bases, and we employed actors to dramatise real-life events. It really brought an edge to the film – made it far more interesting than your normal health and safety film."

The pair decided they could use a similar approach to make Kajaki, their embryonic war film.

With a "shoestring" £1 million budget, all of which needed to be found from private investors, the pair had to think big, but on a small scale in film terms.

"We did the same thing as we'd done with the health and safety films, we went out there and interviewed each of the 11 survivors of that day. As a screenwriter it was far easier than writing fiction. The men started speaking, and the extraordinary things that happened to them just came out – it was stuff I simply couldn't have made up."

But the biggest pitch of Tom's career so far came when he had to approach the parents of the late Corporal Mark Wright with the idea.

"We needed their blessing to do the film," he says. "So we went up to Edinburgh, and spent the day with them – looking through family photo albums, watching home videos of Mark, and explaining exactly what we wanted to do with the film. We wanted to tell his extraordinary story of heroism. I remember Mark's dad saying 'this has to be made'."

After years of planning, almost half the budget is now in place, meaning filming can begin in May.

"We've found an excellent filming location, near a dam in Jordan, and so it's all going to happen quickly now. We wanted to get the film finished and out there for this year, as the draw-down of troops is taking place. The returning soldiers themselves need to be our initial audience with this movie. If they don't watch it, then nobody will. That's why the pressure is really on my shoulders to make sure it's accurate and believable to those guys who have been there.

"It isn't going to be a film 'based on a true story' – it is going to be the true story," he adds. "Having said that, we see it as being something like Jaws to watch, if that doesn't sound too insensitive to say under the circumstances. But it's going to be all about one location, an incredible amount of tension, and a human story of overcoming the most horrendous of situations."

Now all that remains is for the team behind the project to find the remaining half a million pounds of funding.

"We've been crowdfunding online, and we've raised an incredible £30,000 in small donations – £10, £20, £100 and so on, and a lot of that has come from serving soldiers. But we've also been targeting big investors who are buying into the film as a business venture. So there are two strands of funding developing out there.

"But ultimately I think the money will be found," Tom says with a shrug, as his eyes wander back towards the soldiers running up the hill outside his window. "I'm confident there are enough people out there who think, like me, that these extraordinary tales of modern-day heroism really do need to be told."

For more information about the movie, or to find out how you can donate to the film, visit the website at www.kajakimovie.com The final day for small-scale crowdfunding donations is Monday